Wide belt sanding machine with improved dust collector

ABSTRACT

An endless abrasive belt sanding machine in which the sanding or abrading head is vertically oriented and provided with an improved dust collecting system having a suction duct connected with a source of suction and a mouth located in a closed zone partially defined by the portion of the abrasive belt leaving work performing engagement with the workpiece, and into which zone air can enter only through an air supply duct that overlies the upwardly traveling stretch of the abrasive belt and has its inlet defined by a curved hood embracing the belt tensioning roll at the top of the abrading head, and has its discharge arranged to cause the air debouching therefrom to forcibly impinge the surface of the abrasive belt directly above the mouth of the suction duct. A movable wall separates the discharge end of the air supply duct from the mouth of the suction duct and serves as a damper that can be closed to prevent entry into the suction duct of extraneous matter capable of igniting the contents of the separator and dust collecting bags to which the dust and products of abrasion are delivered when the machine is operating normally.

[451 Mar. 25, 1975 United States Patent [1 1 Schuster WIDE BELT SANDINGMACHINE WITH IMPROVED DUST COLLECTOR [75] Inventor: Gordon L. Schuster,Minneapolis,

Minn.

[73] Assignee Timesavers Inc Minneapolis provided with an improved dustcollecting system hav- Minn.

ing a suction duct connected with a source of suction and a mouthlocated in a closed zone partially defined by the portion of theabrasive belt leaving work per- {22] Filed: Feb. 7, 1974 Appl. No.:440,391

forming engagement with the workpiece, and into which zone air can enteronly through an air supply duct that overlies the upwardly travelingstretch of the abrasive belt and has its inlet defined by a curved hoodembracing the belt tensioning roll at the top of the abrading head, andhas its discharge arranged to 36 2 70 5 2 2 /5 8 1 3 41 3 n 7 76 152 811 v0 UR R 2 5 5-03 4 7 2 2 1 5 5 .5 mmh uC .r. ""3 U .I C smflm UIF mum555 cause the air debouching therefrom to forcibly impinge the surfaceof the abrasive belt directly above the mouth of the suction duct. Amovable wall sepa- [56] References Cited UNITED STATES PATENTS rates thedischarge end of the air supply duct from the 51/139 X mouth of thesuction duct and serves as a damper that 51/273 can be closed to prevententry into the suction duct of 51/135 R extraneous matter capable ofigniting the contents of 51/135 X the separator and dust collecting bagsto which the 144/252 R dust and products of abrasion are delivered whenthe machine is operating normally.

Primary Examiner-Al Lawrence Smith Assistant ErammerN1cholas P Godicl 24Claims, 6 Drawing Figures PATENTEU 2 5 5 FlG.2.

PATENTEDMAR25I975 3. 872.627

sum u (1F 6 FICA.

PMENTEB MAR 2 51975 sum 5 95 F'IG.5,

WIDE BELT SANDING MACHINE WITH IMPROVED DUST COLLECTOR This inventionrelates to abrading machines and refers more particularly to endlessabrasive belt sanding machines of the type widely used in thewoodworking industry. Such machines usually have a vertically orientedabrading head with a wide endless abrasive belt trained over a powerdriven contact drum at the bottom and an idler belt tensioning roll atthe top, so that the belt has upwardly and downwardly travelingstretches. The contact drum holds the belt against the work passingthrough the machine. Needless to say, the abrasion of the work by therapidly traveling belt generates an enormous amount of dust.Accordingly, it is an absolute necessity that sanding machines beequipped with dust collecting systems.

Conventionally, the dust collecting systems of sanding machines consistsimply of a cyclone separator and two suction ducts, one leading to theseparator from a suction mouth located in the machine near the zone ofaction and the other connecting a hood over the top of the abrading headwith the separator.

While those prior dust collecting systems did succeed in removing mostof the dust and products of abrasion from sanding machines, they werenotoriously inefficient since they required the movement of a very highvolume of air often in excess of 4,500 cubic feet per minute to effectthat removal. In addition, they necessitated a static pressuredifferential as high as six inches of water column at the point thesuction ducts were connected to the machine. Obviously the powerrequired to meet these needs was substantial.

The cyclone separators were usually mounted on the roof of the buildingin which the sanding machines were housed, or at least were so locatedthat the air leaving the separator and theoretically freed of dust wasdischarged into the atmosphere. Since that air was not in fact free ofminute dust particles, it constituted a serious source of air pollution.Government regulations no longer countenance that practice, and to meetthose regulations the air debouching from the separators now must beducted to a bag room where it enters huge vacuum cleaner bags thatfilter the tiny air-entrained particles from the air before it ispermitted to enterthe atmosphere. The power required to push the airthrough the walls of the collector bags increases as the volume of airmoved rises, so that any significant reduction in that volume wouldresult in increased efficiency.

In the search for improvement in the efficiency of dust collectingsystems, it was discovered that the manner in which the air enters thezone from which the dust and products of abrasion are withdrawn has agreat deal to do with the efficiency of the system. Prior dustcollectors had no provision for controlling the air entering this zone.In fact, it was not known how this occurred.

With a view toward implementing the aforesaid discovery, it is an objectof this invention to prevent entry of air into the zone of action wherethe dust and products of abrasion are generated, except through an airsupply duct that not only debouches directly into the zone of action butalso causes the incoming air to forcibly impinge upon the surface of theabrasive belt directly above the bottom of its upwardly travelingstretch.

Another object of this invention, aimed at improving the efficiency ofthe dust collecting systems of sanding machines, is to use the same airstream to remove dust and products of abrasion from the region at thetop of the abrading head as well as from the zone of action at thebottom of the abrading head, and to that end the dust collector of thisinvention features an air supply duct that overlies the entire upwardlytraveling stretch of the abrasive belt and has its inlet defined by acurved hood that embraces the belt tensioning roll at the top of theabrading head.

Since the overall height of the abrading head in a sanding machinedepends upon the length of its abrasive belt, and since that dimensionwill vary from belt to belt, the invention has as another of its objectsto connect the curved air inlet hood with the air supply duct into whichit discharges in a manner that enables the hood to ride up and down withchanges in the elevation of the top of the abrading head, so that apredetermined positional relationship can be maintained therebetweenregardless of the length of the abrasive belt.

Accidental breakage of the abrasive belts of sanding machines, thoughnot common, does occur and, when it does, the consequences can be veryserious. The possibility of fire is a hazard that has always worried thewoodworking industry. All possible precautions are taken to prevent it,but heretofore there has been no known way of guarding against firesbeing started by fragments of the abrasive belt being drawn into thesuction ducts of the dust collecting systems upon accidental breakage ofthe belt. lnvariably, such fragments are extremely hot and can ignitethe dust in the collecting system in a flash.

In recognition of that danger, the present invention has as another ofits objectives to provide means for closing the mouth of the suctionduct.

With these observations and objectives in mind, the manner in which theinvention achieves its purpose will be appreciated from the followingdescription and the accompanying drawings, which exemplify theinvention, it being understood that changes may be made in the specificapparatus disclosed herein without departing from the essentials of theinvention set forth in the appended claims.

The accompanying drawings illustrate one complete example of theembodiment of the invention constructed according to the best mode sofar devised for the practical application of the principles thereof, andin which:

FIG. 1 is a perspective view of a sanding machine equipped with the dustcollecting system of this invention;

FIG. 2 is a side view of the machine with parts broken away and insection;

FIG. 3 is a sectional view through the lower end portion of the airsupply and suction ducts and showing the relationship thereof to thecontact drum-supported abrasive belt;

FIG. 4 is a perspective view of the air supply and suction ductassembly, viewing the same from the side that faces the upwardlytraveling stretch of the abrasive belt;

FIG. 5 is a perspective view of the structure shown in FIG. 4, butviewing the same from the opposite side; and

FIG. 6 is a side view similar to FIG. 2, but illustrating an additionalfeature of the invention.

Referring to the accompanying drawings, the numeral designates generallythe main frame of a wide belt sanding machine, in the upper portion ofwhich there is a conventional abrading head 11 and below it a workfeeding assembly 12.

The main frame which is preferably a weldment has a base section 14 andspaced side sections 15 and 16 rising therefrom. Rigidly fixed to theside section 16 and extending cantilever fashion therefrom towards theother side of the machine is a horizontal arm 17, which in the industryis known as a center bar. It is the center bar that carries the abradinghead.

Since the abrading head is conventional, it comprises an endlessabrasive belt 18 trained over a contact drum 19 at the bottom of thehead and an idler roll 20 at the top. As shown and described in theBernu Pat. No. 3,777,442, which is issued to the assignee of the presentinvention, the contact drum 19 is journaled in bearings that are fixedto and project down from the center bar, and the idler roll 20 isjournaled in bearings 21 on the arms of a yoke 22 that is supportedabove the center bar by the ram 23 of an air cylinder mounted on thecenter bar. In this manner, the idler roll 20 can be raised to tensionthe abrasive belt and lowered to enable the same to be removed andreplaced when necessary.

The contact drum 19 at the bottom of the abrading head is drivinglyconnected with a motor (not shown) and imparts high speed orbital motionto the abrasive belt in the counterclockwise direction, as viewed inFIGS. 2 and 3. The belt thus has upwardly and downwardly travelingstretches indicated by the arrows U and D in FIG. 2.

It is the contact drum that holds the arasive belt against the surfaceof the workpieces as they are carried through the machine by an endlesspower driven conveyor belt 24 which forms part of the work feedingassembly 12. By virtue of the counterclockwise rotation of the contactdrum, the dust and products of abrasion that result from the workperforming engagement between the abrasive belt and the workpieces, arethrown upstream with respect to the direction the workpieces movethrough the machine and upwardly.

along the upwardly traveling stretch of the abrasive belt.

As is customary, the elevation of work feeding assembly 12 is adjustableto accommodate different thicknesses of work. The mechanism by whichthat adjustment is made comprises a plurality ofjack screws on which theassembly 12 is supported and which are simultaneously actuatable byrotation ofa handwheel 25. With the elevation of the work feedingassembly properly set, the workpieces one of which is shown in FIG. 2are gripped between superimposed top and bottom pinch rolls 26 and 27respectively, the former being mounted in the main frame of the machineat the infeed and outfeed sides of the abrading head and the latterbeing part of the work feeding assembly. As is customary, the upperpinch rolls are yieldingly biased downwardly to press the work againstthe work feeding conveyor belt.

There are also infeed and outfeed pressure shoes 28 and 29,respectively, to hold the work down as close as possible to the line ofcontact between the abrasive belt and the workpiece as the latter firstcomes into contact with the belt and as it leaves the same. These shoesare mounted between side plates that are a fixed part of the machineframe, and extend across the entire width of the abrasive belt. Like thetop pinch rolls, the work engaging toe portions of the shoes areyieldingly pressed against the work.

From the standpoint of this invention, it is important to note that theinfeed shoe 28 has a concave curved surface relatively close to theadjacent portion of the abrasive belt. While that relationship is notnew, its existence is utilized in achieving one of the objectives of theinvention, as will appear as the description proceeds.

As in prior dust collecting systems of wide belt sanding machines, thedust and products of abrasion generated by the machine in operation aredrawn from the zone of action through a suction duct 30 that has itsmouth 31 closely adjacent to the bottom of the abrading head, and itsdischarge end connected by a pipe 32 with a cyclone separator (notshown). The separator provides a source of suction to draw the dust andproducts of abrasion into the mouth 31 of the suction duct, as it did inall prior dust collecting systems. But contrary to prior dust collectorswhich had no provision for controlling admission of make-up air to thezone from which the mouth of the suction duct drew the airentrained dustand products of abrasion the present invention not only controls theadmission of make-up air to that zone but, in addition, utilizes itsentry to sweep dust and products of abrasion off of the abrasive belt.

To this end, the make-up air is fed to the zone of action through anupright air supply duct 33 that overlies and is coextensive in size andshape with the upwardly traveling stretch of the abrasive belt. Theinlet to this air supply duct is defined by a curved hood 33 thatembraces the belt tensioning roll 20 at the top of the abrading head,and its outlet is directly above the mouth 31 of the suction duct.

The air supply duct 33 has flat front and rear walls 34 and 35,respectively, connected by narrow, parallel side walls 36, and as bestseen in FIGS. 4 and 5 the two ducts are joined together into a unitarystructure with the rear wall 35 of the air supply duct forming the frontwall of the suction duct. Since the pipe 32 that leads to the cycloneseparator is round, the side walls 37 of the suction duct convergetoward the top of the duct and its rear wall 38 diverges from the wall35 so that the cross sectional area of the suction duct remainssubstantially uniform from top to bottom. A transition section 39 at thetop of the suction duct gradually changes its cross sectional shape fromrectangular to round to make possible its connection to the pipe 32. j

The unitary duct structure comprising the joined air supply and suctionducts is suitably mounted in the machine with the front wall 34 of theair supply duct closely adjacent to and parallel with the upwardlytraveling stretch of the abrasive belt and the transition section 39 ofthe suction duct protruding from the top of the machine. This places thetop of the air supply duct at a level near that of the axis of the belttensioning roll 20 when the abrasive belt is of average length, butsince belt length varies, the elevation of the roll 20 will changeaccordingly. Therefore, in order for the curved hood 33 which definesthe inlet to the air supply duct to occupy a predetermined position withrespect to the top of the abrading head, it is hingedly connected, as at40, to the back wall 35 of the air supply duct and rests on castorsmounted in brackets 41 that are fixed to the bearings 21 in which theroll is journaled. In this way, the bottom wall 42 of the curved hoodwill always be spaced the same distance above the top of the abradinghead, despite variations in the elevation of the roll 20; and to assurecontinuity between the hood and the air supply duct, the discharge endof the former extends a short distance into the top of the air supplyduct.

Attention is directed to the location of the front edge 43 of the bottomwall of the curved hood. It is spaced back from the front edges of theside and top walls of the hood and lies between the crest of the top ofthe abrading head and the start of the downwardly traveling stretch ofthe abrasive belt. Hence dust and products of abrasion that are thrownfrom the belt by centrifugal force as the belt travels over the roll 20,can enter the inlet of the hood.

To assist in directing such dust and products of abrasion into the hood,a deflector unit 44 is secured at its ends to the side walls of the hoodand spans the distance therebetween ahead of the front edge 43 of thehood bottom wall.

All of the dust that in prior dust collecting systems was drawn from theregion above the top of the abrading head by a separate dust hoodconnected with a source of suction, by this invention is carried fromthat region by the air stream entering the air supply duct through thecurved hood.

Since the mouth of the suction duct is located in the zone where thedust and products of abrasion are generated, most of it by far is drawninto the suction duct, but that which is not will be carried along bythe upwardly traveling stretch of the abrasive belt. By virtue of itslocation closely adjacent to this stretch of the belt, the air supplyduct coacts with the belt to confine the rising dust particles to a paththat leads to the region above the abrading head from which the make-upair is drawn. For all practical purposes, therefore, all of the dust andproducts of abrasion that are generated during the operation of themachine are carried into the suction duct by the same air stream.

One of the most important aspects of the invention and to a large degreethe reason why it has so significantly increased the efficiency of thedust collector, resides in the fact that the zone from which the mouthof the suction duct draws the air and the air-entrained dust andproducts of abrasion, is substantially closed against entry of airthereto, except through the air supply duct 33. To this end, the sidewall 36 of the air supply duct at the far side of the machine in FIGS. 2and 3, has an extension 45 with a convexly curved bottom edge 46 thatlies closely adjacent to the concavely curved top surface of the infeedshoe 28. At the near side of the machine, there is a similar downwardextension 47 of the adjacent side wall of the air supply duct, but thisextension is hingedly mounted, as at 47, to enable the same to be liftedwhen access to the suction zone is necessary.

The infeed shoe 28 and the downward extensions 45 and 47 of the sidewalls of the air supply duct thus coact with one another and with theadjacent abrasive belt to restrict unwanted entry of air into thesuction zone, and to further guard against such unwanted entry of airinto the suction zone, the side walls and back wall of the suction ductproject downwardly far enough to coact with the extensions 46 and 47 andwith the infeed shoe.

Another factor in the control of air admission to the suction zone isthe close proximity of the front edges 48 of the extensions 45 and 47 tothe upwardly traveling stretch of the abrasive belt. To minimize thehazard of fire resulting from sparking, these front edges of theextensions are covered with shields 49 of non-sparking material, such asaluminum. For the same reason the front wall 34 of the air supply duct33 is covered with an aluminum shield 34.

Just above its outlet, the air supply duct is reduced in cross sectionto increase the velocity of the discharging make-up air. This reductionor constriction results essentially from the securement of a shallowV-shaped wall section 50 to the inside surface of the front wall 34 ofthe air supply duct. This V-shaped wall section extends from side wallto side wall of the air supply duct and has its downstream flange 51extended beyond the bottom edge of the front wall 34 to define the upperedge of the narrow elongated outlet of the air supply duct. As in thecase of the front edges of the downward extensions 45 and 47, theunderside of the flange 51 has a shield 51' of nonsparking metal appliedto it. The foremost edge of this shield which extends across the fullwidth of the abrasive belt, is closely adjacent to the belt, the spacingtherebetween being on the order of one-eighth of an inch. Accordingly,dust and products of abrasion are stripped off of the upwardly travelingstretch of the belt by the shield 51.

The bottom edge of the narrow elongated outlet of the air supply duct isformed by a rectangular wall or plate 52 that is hingedly connected to apair of brackets 53 suitably fixed to the frame of the machine inembracing relation with the air supply and suction ducts. These bracketsalso form part of the structure by which the air supply and suction ductassembly is mounted.

Specifically, the hinged mounting of the plate 52 comprises a rod 54that is welded to one edge of the plate and has its end portionsjournaled in holes in the brackets 53. The plate 52 spans the distancebetween the side walls 36 of the air supply duct, so that by virtue ofits hinged mounting the plate forms a damper common to both the outletof the air supply duct and the mouth of the suction duct. In fact, thisdamper separates the two ducts from one another at the point of theircommunication.

Being located inwardly of the rear wall 35 of the air supply duct andopposite the V-shaped wall section 50, the rod 54 coacts with the apexof the V-shaped wall section to form the constriction by which thevelocity of the air discharging from the air supply duct is increased.To smoothly guide the air flow past the rod 54, the bottom edge portionof the rear wall 35 is bent forwardly and then upwardly at an angle toform a sloping wall section 55 that lies opposite the upper flange ofthe V-shaped wall section 50, and is in downward convergent relationtherewith. A thin resiliently flexible metal strip 56 fixed to thesloping wall section 55 and projecting downwardly therefrom, assuresagainst loss of make-up air through the inevitable clearance between therod 54 and the bottom of the rear wall 35.

A lever 57 fixed to one end of the rod 54 and connected with the pistonof an air cylinder 58 by a link 59 provides power means for swinging thedamper 52 between its normal or open position shown in full lines inFIG. 3 and a closed position indicated in dotted lines. In the latter ofthese positions, the damper essentially closes the mouth of the suctionduct to prevent entry intothat duct of extraneous matter that couldcause highly dangerous consequences. This is therefore a veryadvantageous and valuable feature of the invention, since it greatlyminimizes the tire hazard by excluding from the suction duct hotfragments of a broken belt that could ignite the dust in a flash.

While activation of the valves that govern connection of the aircylinder with a source of air pressure can be left entirely to manualcontrol, it is preferable to employ for that purpose an automaticcontrol that is responsive to strategically located sensing means whichdetect the occurrence of accidents such as breakage of the abrasivebelt, and even manual shut-down of the machine. Since such controls canbe of any conventional type, they have not been illustrated, but merelyindicated by the box AC in FIG. 2.

In its normal open position, the damper 52 is parallel to the lowerflange 51 of the V-shaped wall section 50 and coacts therewith to directthe high velocity air debouching from the air supply duct against thearea of the upwardly traveling stretch of the abrasive belt that liesjust above the line of tangency between the belt and the contact drum.The angle at which the air forcibly impinges upon the abrasive belt hasbeen found to be critical. It should be between 38 and 45, as indicatedin FIG. 3.

With the damper in its normal open position, its free edge is close tothe abrasive belt and coacts therewith to define a restricted throatthrough which the air must pass to reach the mouth of the suction ductand, in doing so, the air exerts a powerful wiping action on the beltsurface. To minimize turbulence in the air as it passes around the freeedge of the damper, that edge has a smooth surfaced shield 60 appliedthereto and, for protection against sparking, this shield is formed ofaluminum. The medial portion of the shield which embraces the edge ofthe damper is convexly curved to eliminate abrupt changes in directionof the air flow.

As is customary in sanding machines, the abrading head is enclosed in acabinet-like housing 61 having upright walls fixed to the frame of themachine and a hinged door 62 which, when open, affords access not onlyto the abrading head for removal and replacement of sanding belts, butalso to the dust collector and its appurtenances. Air enters the housing61 through an inlet hood 63 on its top wall.

In the preferred embodiment of the invention, the air supply and suctionducts connected as they are into a unitary structure are fixedly mountedwhich makes the placement and removal of abrasive belts slightlydifficult. To remove that objection, the duct structure can be mountedto swing from its operative position to a retracted position spacedfarther away from the abrading head, as in FIG. 6. For this purpose, theduct structure is carried by upper and lower paired arms 65 and 66,respectively, that are pivoted to brackets fixed to the frame of themachine. An air cylinder 67 suitably mounted at each side of the machinewith its piston connected to the adjacent lower arm 66 through a link68, provides power means to shift the duct structure from .one positionto the other.

The increase in the efficiency of dust collecting systems which thisinvention has achieved, is evidenced by the fact that it requires only1500 cubic feet of air per minute (1,500 CFM) to remove all of the dustand products of abrasion in a sanding machine that, with prior dustcollectors, required 4500 cubic feet of air per minute (4,500 CFM) to dothe same job.

Other evidence of the improvement accomplished by this invention is thereduction in the static pressure differential needed to move the air,from 6 to 4 inches of water column.

The saving in power requirements are therefore quite substantial and,since this invention also has eliminated the heretofore required dustcollecting hood above the abrading head, there is also a significantreduction in the cost of the dust collecting system.

Those skilled in the art will appreciate that the invention can beembodied in forms other than as herein disclosed for purposes ofillustration.

The invention is defined by the following claims:

I claim: I

1. In an abrading machine having a substantially vertically orientedabrading head that has a power driven endless abrasive belt withupwardly and downwardly traveling stretches, held against work fedthrough the machine by a backup member located at the bottom of theabrading head, improved dust collecting means for removing the dust andproducts of abrasion incident to operation of the machine, and whichcomprises the combination of:

A. a vertically oriented air supply duct adjacent to the upwardlytraveling stretch of the abrasive belt, the inlet to said air supplyduct being at its top and the outlet at its bottom;-

B. means at the outlet of the air supply duct to cause the air issuingtherefrom to impinge upon the abrasive belt in a zone located a shortdistance above the bottom of the upwardly traveling stretch of the belt;

C. a suction duct connectable with a source of suction and having itsmouth contiguous to the outlet of the air supply duct to draw air, dustand the products of abrasion from said zone; and

D. closure means coacting with the abrasive belt to restrict access tosaid zone and thereby minimize the possibility of air entering said zoneexcept through the air supply duct.

2. In an abrading machine, the invention defined by claim 1, wherein theoutlet of the air supply duct is a narrow slot with parallel upstreamand downstream edges that extend across the width of the abrasive belt,the upstream edge being spaced from but sufficiently close to theupwardly traveling stretch of the abrasive belt to enable said edge toeffect removal of dust and products of abrasion carried along by thebelt and to cause the same to be entrained by the air issuing from theoutlet of the air supply duct; and wherein the mouth of said suctionduct is directly below the outlet of the air supply duct and extendsacross the width of the abrasive belt and communicates with said zonethrough the space between the mouth of the suction duct and the abrasivebelt.

3. In an abrading machine, the invention defined by claim 2, wherein thedownstream edge of the outlet of the air supply duct coacts with theabrasive belt to define the size of the space communicating said zonewith the mouth of the suction duct.

4. In an abrading machine, the invention defined by claim 3, wherein themeans at the outlet of the air supply duct that causes the air issuingtherefrom to im' pinge upon the abrasive belt is a substantiallyrectangular wall with opposite top and bottom edges and opposite endedges, the bottom edge of said substantially rectangular wall being thedownstream edge'of the outlet of the air supply duct.

5. In an abrading machine, the invention defined by claim 4, wherein thebottom edge of said substantially rectangular wall is defined by asmooth convexly curved surface.

6. In an abrading machine, the invention defined by claim 4, wherein thesize of the mouth of the suction duct is determined by the distance thebottom edge of said substantially rectangular wall is from the abrasivebelt; and further characterized by hinge means at an elevation abovethat of the upstream edge of the outlet of the air supply duct connectedwith the top edge of said substantially rectangular wall to mount saidwall for swinging motion between a wide open position in which itsbottom edge is close to the abrasive belt and the mouth of the suctionduct is of maximum size and a closed position in which said bottom edgeis remote from the abrasive belt and the mouth of the suction duct isessentially closed.

7. In an abrading machine having an abrading head with a power drivenendless abrasive belt and a backup 1 member engaging the back of thebelt to hold the same against the surface of a workpiece being abraded,and also having a suction duct to carry off dust and products ofabrasion incident to operation of the machine, said machine beingcharacterized by:

A. means mounting said suction duct with its mouth closely adjacent tothe backup member and hence at the source of the dust and products ofabrasion;

B. an air supply duct having its inlet remote from the back-up memberand its outlet adjacent to the inlet of the suction duct;

C. a door at the mouth of the suction duct that is movable between afirst position directing the air issuing from the outlet of the airsupply duct against the adjacent surface of the abrasive belt and asecond position essentially closing the mouth of the suction duct toprevent entry into the suction duct of extraneous matter capable ofcausing serious consequences if permitted to enter the suction duct; and

D. means for moving said door from one to the other of said positions.

8. The abrading machine of claim 7, wherein the means for moving. saiddoor is manually operable.

9. The abrading machine of claim 7, wherein the means for moving saiddoor to its second position is controlled by sensing means responsive tothe occurrence of any one of a number of events, such as breakage of theabrasive belt or any othermalfunctioning of the abrading head, andmanual shut-down of the machine,

and wherein the detection of such an event by the sensingmeansautomatically effects movement of the door to its second position.

10. In an abrading machine having a vertically oriented abrading headwith a power driven endless abrasive belt trained over a belt tensioningroll at the top of the head and held against the work being abraded by abackup member at the bottom of the head, so that the belt has upwardlyand downwardly traveling stretches, improved dust collecting means forremoving the dust and products of abrasion incident to operation of themachine, comprising:

A. a suction duct connectable with a source of suction and having amouth in juxtaposition to the backup member to suck the air-entraineddust and products of abrasion from the zone in which they are produced;

B. an air supply duct having its inlet adjacent to the belt tensioningroll and its outlet directly above the mouth of the suction duct andfacing the upwardly traveling stretch of the abrasive belt;

C. a movable door adjacent to the outlet of the air supply duct and themouth of the suction duct operable in one position thereof to direct theair issuing from the outlet of the air supply duct against the adjacentsurface of the abrasive belt and in another position to close saidmouth-and thereby prevent entry into the suction duct of extraneousmatter capable of causing objectionable consequences if permitted toenter the suction duct; and

D. means for moving said door from one to the other of said positions.

11. The abrading machine of claim 10, wherein said movable door has ahingedly mounted edge and a free edge, the latter coacting with theabrasive belt to define a constricted throat that communicates the airsupply duct with the suction duct.

12. The abrading machine of claim 10, further characterized by:

means including said movable door to cause the air debouching from theair supply duct to forcibly impinge upon the upwardly traveling stretchof the abrasive belt.

13. In an abradingmachine having a vertically oriented abrading headwith a power driven endless abrasive belt trained over a belt tensioningroll at the top of the head and held against the work being abraded by abackup member at the bottom of the head, so that the belt has upwardlyand downwardly traveling stretches, improved dust collecting means forremoving the dust and products of abrasion incident to operation of themachine, comprising:

A. a suction duct connectable with a source of suction and having amouth in juxtaposition to the backup member to suck the air-entraineddust and products of abrasion from the Zone in which they are produced;

B. an air supply duct through which air is brought to said zone, saidair supply duct having an outlet directly above the mouth of the suctionduct; and

C. air directing means at the outlet of the air supply duct to cause theair entering said zone to impinge upon the upwardly traveling stretch ofthe abrasive belt as the belt leaves the backup member at an angle ofbetween 38 and 45 to the upwardly traveling stretch of the belt.

14. The abrading machine in claim 13, wherein the backup member is acontact drum, andwherein the air directing means causes the air toimpinge upon the abrasive belt directly above the line of tangencybetween the upwardly traveling stretch of the belt and the contact drum.

15. In an abrading machine having a vertically oriented abrading headwith a power driven endless abrasive belt trained over a belt tensioningroll at the top of the head and held against the work being abraded by abackup member at the bottom of the head, so that the belt has upwardlyand downwardly traveling stretches, improved dust collecting means forremoving the dust and products of abrasion incident to operation of themachine, comprising:

A. an air supply duct having inlet and outlet ends,

and opposite inner and outer walls, at least the former of said wallsbeing substantially coextensive in size and shape with the upwardlytraveling stretch of the abrasive belt;

B. a curved air inlet duct having an entrance and an exit;

C. a suction duct having an outlet connectable with a source of suctionand a mouth through which airentrained dust and products of abrasion aredrawn into the suction duct when the machine is in operation;

D. means joining said ducts into a unitary structure with the exit ofthe curved air inlet duct opening into the inlet end of the air supplyduct and with the suction duct overlying said outer wall of the airsupply duct and its mouth contiguous to the outlet end of the air supplyduct; and

E. means mounting said unitary structure in an operative positionadjacent to the abrading head, in which position said inner wall of theair supply duct overlies and is closely adjacent to the upwardlytraveling stretch of the abrasive belt, the curved air inlet ductembraces the belt tensioning roll and the entrance thereof is positionedto receive air from the space surrounding the belt tensioning roll andalso receive air-entrained dust and products of abrasion leaving thepassing abrasive belt, and the outlet end of the air supply duct and themouth of the suction duct are contiguous to the backup member at thebottom of the abrading head, so that the same air moving through theducts carries away dust and products of abrasion from both the zone ofaction where the abrasion takes place and from the zone at the top ofthe abrading head.

16. The abrading machine of claim 15, wherein said means mounting saidunitary structure provides for bodily movement thereof from its definedoperative position to a retracted position to facilitate access to theabrading head,

and further characterized by means for effecting such bodily movement ofsaid unitary structure from and back to its defined operative position.

17. In an abrading machine having an abrading head with a power drivenendless abrasive belt trained over a belt tensioning roll and heldagainst the work being abraded by a backup member engaging the back ofthe belt, improved dust collecting means for carrying off dust andproducts of abrasion incident to operation of the machine, said dustcollecting means comprising:

A. an air supply duct overlying a stretch of the abra sive belt andhaving its inlet adjacent to the belt tensioning roll and its outletopening to a zone adjacent to the backup member;

B. a suction duct connectable with a source of suction and having itsmouth contiguous to the outlet of the air supply duct to draw air, dustand products of abrasion from said zone; and

C. closure means coacting with the abrasive belt to restrict access tosaid zone and thereby minimize the possibility of air entering said zoneexcept through the air supply duct.

18. the invention defined in claim 17, further characterized by:

structure connected with the inlet of the air supply duct arranged todirect dust and products of abrasion that reach the zone in which thebelt tensioning roll is located into the air stream entering the inletof the air supply duct.

19. The invention defined in claim 18, wherein the abrading head isvertically oriented with its belt tensioning roll at the top and itsbackup member at the bottom, so that the abrasive belt has upwardly anddownwardly traveling stretches,

and wherein the air supply duct has opposite walls,

one of which is uniformly closely spaced from and substantiallycoextensive in size and shape with the upwardly traveling stretch of theabrasive belt,

so that the air supply duct coacts with the upwardly traveling stretchof the abrasive belt to form a passage through which dust and productsof abrasion that are carried along by the upwardly traveling stretch ofthe belt reach the zone in which the belt tensioning roll is located.

20. The invention defined in claim 18, wherein the abrading head isvertically oriented with its belt tensioning roll at the top and itsbackup member at the bottom, so that the abrasive belt has upwardly anddownwardly traveling stretches,

wherein the air supply duct is upright and overlies the upwardlytraveling stretch of the abrasive belt,

wherein the inlet of the air supply duct is at a fixed level near theline of tangency between the upwardly traveling stretch of the abrasivebelt and the belt tensioning roll,

said inlet having a narrow oblong shape, the long margins of which aregenerally parallel to the axis of the belt tensioning roll and extendfor substantially the width of the abrasive belt, one of said longmargins being farther from the belt than the other,

and wherein said structure connected with the inlet of the air supplyduct comprises a hood embracing the top of the belt tensioning roll,

said hood having an inlet and an outlet and being defined in part by atop wall which is joined to said long margin that is farthest from thebelt.

21. The abrading machine of claim 20, wherein the hood has top andbottom curved walls connected by opposite side walls to form a curvedextension of the upright air supply duct,

the hood having an inlet remote from its connection with said uprightair supply duct, and the bottom curved wall of the hood being relativelyclose to the cylindrical surface of the belt tensioning roll.-

22. The abrading machine of claim 21, wherein the hood has a hingedconnection with the top of said upright duct, the axis of that hingedconnection being substantially parallel to the axis of the belttensioning roll, and the hood being free to rock about the axis of itshinged connection with the upright duct, and further characterized bysupport means at the top of the abrading head and fixed with respect tothe axis of the belt tensioning roll,

and means on the hood seated upon said support means to positionallyorient the hood with respect to the belt tensioning roll despitevariations in the elevation thereof.

23. The abrading machine of claim 21, further characterized by acterized by deflector means at the inlet to the hood in close juxtapositionto the adjacent surface of the abrasive belt, to intercept dust andproducts of abrasion traveling with the belt and direct the same intothe hood.

1. In an abrading machine having a substantially vertically orientedabrading head that has a power driven endless abrasive belt withupwardly and downwardly traveling stretches, held against work fedthrough the machine by a backup member located at the bottom of theabrading head, improved dust collecting means for removing the dust andproducts of abrasion incident to operation of the machine, and whichcomprises the combination of: A. a vertically oriented air supply ductadjacent to the upwardly traveling stretch of the abrasive belt, theinlet to said air supply duct being at its top and the outlet at itsbottom; B. means at the outlet of the air supply duct to cause the airissuing therefrom to impinge upon the abrasive belt in a zone located ashort distance above the bottom of the upwardly traveling stretch of thebelt; C. a suction duct connectable with a source of suction and havingits mouth contiguous to the outlet of the air supply duct to draw air,dust and the products of abrasion from said zone; and D. closure meanscoacting with the abrasive belt to restrict access to said zone andthereby minimize the possibility of air entering said zone exceptthrough the air supply duct.
 2. In an abrading machine, the inventiondefined by claim 1, wherein tHe outlet of the air supply duct is anarrow slot with parallel upstream and downstream edges that extendacross the width of the abrasive belt, the upstream edge being spacedfrom but sufficiently close to the upwardly traveling stretch of theabrasive belt to enable said edge to effect removal of dust and productsof abrasion carried along by the belt and to cause the same to beentrained by the air issuing from the outlet of the air supply duct; andwherein the mouth of said suction duct is directly below the outlet ofthe air supply duct and extends across the width of the abrasive beltand communicates with said zone through the space between the mouth ofthe suction duct and the abrasive belt.
 3. In an abrading machine, theinvention defined by claim 2, wherein the downstream edge of the outletof the air supply duct coacts with the abrasive belt to define the sizeof the space communicating said zone with the mouth of the suction duct.4. In an abrading machine, the invention defined by claim 3, wherein themeans at the outlet of the air supply duct that causes the air issuingtherefrom to impinge upon the abrasive belt is a substantiallyrectangular wall with opposite top and bottom edges and opposite endedges, the bottom edge of said substantially rectangular wall being thedownstream edge of the outlet of the air supply duct.
 5. In an abradingmachine, the invention defined by claim 4, wherein the bottom edge ofsaid substantially rectangular wall is defined by a smooth convexlycurved surface.
 6. In an abrading machine, the invention defined byclaim 4, wherein the size of the mouth of the suction duct is determinedby the distance the bottom edge of said substantially rectangular wallis from the abrasive belt; and further characterized by hinge means atan elevation above that of the upstream edge of the outlet of the airsupply duct connected with the top edge of said substantiallyrectangular wall to mount said wall for swinging motion between a wideopen position in which its bottom edge is close to the abrasive belt andthe mouth of the suction duct is of maximum size and a closed positionin which said bottom edge is remote from the abrasive belt and the mouthof the suction duct is essentially closed.
 7. In an abrading machinehaving an abrading head with a power driven endless abrasive belt and abackup member engaging the back of the belt to hold the same against thesurface of a workpiece being abraded, and also having a suction duct tocarry off dust and products of abrasion incident to operation of themachine, said machine being characterized by: A. means mounting saidsuction duct with its mouth closely adjacent to the backup member andhence at the source of the dust and products of abrasion; B. an airsupply duct having its inlet remote from the back-up member and itsoutlet adjacent to the inlet of the suction duct; C. a door at the mouthof the suction duct that is movable between a first position directingthe air issuing from the outlet of the air supply duct against theadjacent surface of the abrasive belt and a second position essentiallyclosing the mouth of the suction duct to prevent entry into the suctionduct of extraneous matter capable of causing serious consequences ifpermitted to enter the suction duct; and D. means for moving said doorfrom one to the other of said positions.
 8. The abrading machine ofclaim 7, wherein the means for moving said door is manually operable. 9.The abrading machine of claim 7, wherein the means for moving said doorto its second position is controlled by sensing means responsive to theoccurrence of any one of a number of events, such as breakage of theabrasive belt or any other malfunctioning of the abrading head, andmanual shut-down of the machine, and wherein the detection of such anevent by the sensing means automatically effects movement of the door toits second position.
 10. In an abrading machine having a verticallyoriented abrading head with a power driven endless abrasive belt trainedover a belt tensioning roll at the top of the head and held against thework being abraded by a backup member at the bottom of the head, so thatthe belt has upwardly and downwardly traveling stretches, improved dustcollecting means for removing the dust and products of abrasion incidentto operation of the machine, comprising: A. a suction duct connectablewith a source of suction and having a mouth in juxtaposition to thebackup member to suck the air-entrained dust and products of abrasionfrom the zone in which they are produced; B. an air supply duct havingits inlet adjacent to the belt tensioning roll and its outlet directlyabove the mouth of the suction duct and facing the upwardly travelingstretch of the abrasive belt; C. a movable door adjacent to the outletof the air supply duct and the mouth of the suction duct operable in oneposition thereof to direct the air issuing from the outlet of the airsupply duct against the adjacent surface of the abrasive belt and inanother position to close said mouth and thereby prevent entry into thesuction duct of extraneous matter capable of causing objectionableconsequences if permitted to enter the suction duct; and D. means formoving said door from one to the other of said positions.
 11. Theabrading machine of claim 10, wherein said movable door has a hingedlymounted edge and a free edge, the latter coacting with the abrasive beltto define a constricted throat that communicates the air supply ductwith the suction duct.
 12. The abrading machine of claim 10, furthercharacterized by: means including said movable door to cause the airdebouching from the air supply duct to forcibly impinge upon theupwardly traveling stretch of the abrasive belt.
 13. In an abradingmachine having a vertically oriented abrading head with a power drivenendless abrasive belt trained over a belt tensioning roll at the top ofthe head and held against the work being abraded by a backup member atthe bottom of the head, so that the belt has upwardly and downwardlytraveling stretches, improved dust collecting means for removing thedust and products of abrasion incident to operation of the machine,comprising: A. a suction duct connectable with a source of suction andhaving a mouth in juxtaposition to the backup member to suck theair-entrained dust and products of abrasion from the zone in which theyare produced; B. an air supply duct through which air is brought to saidzone, said air supply duct having an outlet directly above the mouth ofthe suction duct; and C. air directing means at the outlet of the airsupply duct to cause the air entering said zone to impinge upon theupwardly traveling stretch of the abrasive belt as the belt leaves thebackup member at an angle of between 38* and 45* to the upwardlytraveling stretch of the belt.
 14. The abrading machine in claim 13,wherein the backup member is a contact drum, and wherein the airdirecting means causes the air to impinge upon the abrasive beltdirectly above the line of tangency between the upwardly travelingstretch of the belt and the contact drum.
 15. In an abrading machinehaving a vertically oriented abrading head with a power driven endlessabrasive belt trained over a belt tensioning roll at the top of the headand held against the work being abraded by a backup member at the bottomof the head, so that the belt has upwardly and downwardly travelingstretches, improved dust collecting means for removing the dust andproducts of abrasion incident to operation of the machine, comprising:A. an air supply duct having inlet and outlet ends, and opposite innerand outer walls, at least the former of said walls being substantiallycoextensive in size and shape with the upwardly traveling stretch of theabrasive belt; B. a curved air inlet duct having an entrancE and anexit; C. a suction duct having an outlet connectable with a source ofsuction and a mouth through which air-entrained dust and products ofabrasion are drawn into the suction duct when the machine is inoperation; D. means joining said ducts into a unitary structure with theexit of the curved air inlet duct opening into the inlet end of the airsupply duct and with the suction duct overlying said outer wall of theair supply duct and its mouth contiguous to the outlet end of the airsupply duct; and E. means mounting said unitary structure in anoperative position adjacent to the abrading head, in which position saidinner wall of the air supply duct overlies and is closely adjacent tothe upwardly traveling stretch of the abrasive belt, the curved airinlet duct embraces the belt tensioning roll and the entrance thereof ispositioned to receive air from the space surrounding the belt tensioningroll and also receive air-entrained dust and products of abrasionleaving the passing abrasive belt, and the outlet end of the air supplyduct and the mouth of the suction duct are contiguous to the backupmember at the bottom of the abrading head, so that the same air movingthrough the ducts carries away dust and products of abrasion from boththe zone of action where the abrasion takes place and from the zone atthe top of the abrading head.
 16. The abrading machine of claim 15,wherein said means mounting said unitary structure provides for bodilymovement thereof from its defined operative position to a retractedposition to facilitate access to the abrading head, and furthercharacterized by means for effecting such bodily movement of saidunitary structure from and back to its defined operative position. 17.In an abrading machine having an abrading head with a power drivenendless abrasive belt trained over a belt tensioning roll and heldagainst the work being abraded by a backup member engaging the back ofthe belt, improved dust collecting means for carrying off dust andproducts of abrasion incident to operation of the machine, said dustcollecting means comprising: A. an air supply duct overlying a stretchof the abrasive belt and having its inlet adjacent to the belttensioning roll and its outlet opening to a zone adjacent to the backupmember; B. a suction duct connectable with a source of suction andhaving its mouth contiguous to the outlet of the air supply duct to drawair, dust and products of abrasion from said zone; and C. closure meanscoacting with the abrasive belt to restrict access to said zone andthereby minimize the possibility of air entering said zone exceptthrough the air supply duct.
 18. the invention defined in claim 17,further characterized by: structure connected with the inlet of the airsupply duct arranged to direct dust and products of abrasion that reachthe zone in which the belt tensioning roll is located into the airstream entering the inlet of the air supply duct.
 19. The inventiondefined in claim 18, wherein the abrading head is vertically orientedwith its belt tensioning roll at the top and its backup member at thebottom, so that the abrasive belt has upwardly and downwardly travelingstretches, and wherein the air supply duct has opposite walls, one ofwhich is uniformly closely spaced from and substantially coextensive insize and shape with the upwardly traveling stretch of the abrasive belt,so that the air supply duct coacts with the upwardly traveling stretchof the abrasive belt to form a passage through which dust and productsof abrasion that are carried along by the upwardly traveling stretch ofthe belt reach the zone in which the belt tensioning roll is located.20. The invention defined in claim 18, wherein the abrading head isvertically oriented with its belt tensioning roll at the top and itsbackup member at the bottom, so that the abrasive belt has upwardly anddownwardly traveling stretches, wherein the Air supply duct is uprightand overlies the upwardly traveling stretch of the abrasive belt,wherein the inlet of the air supply duct is at a fixed level near theline of tangency between the upwardly traveling stretch of the abrasivebelt and the belt tensioning roll, said inlet having a narrow oblongshape, the long margins of which are generally parallel to the axis ofthe belt tensioning roll and extend for substantially the width of theabrasive belt, one of said long margins being farther from the belt thanthe other, and wherein said structure connected with the inlet of theair supply duct comprises a hood embracing the top of the belttensioning roll, said hood having an inlet and an outlet and beingdefined in part by a top wall which is joined to said long margin thatis farthest from the belt.
 21. The abrading machine of claim 20, whereinthe hood has top and bottom curved walls connected by opposite sidewalls to form a curved extension of the upright air supply duct, thehood having an inlet remote from its connection with said upright airsupply duct, and the bottom curved wall of the hood being relativelyclose to the cylindrical surface of the belt tensioning roll.
 22. Theabrading machine of claim 21, wherein the hood has a hinged connectionwith the top of said upright duct, the axis of that hinged connectionbeing substantially parallel to the axis of the belt tensioning roll,and the hood being free to rock about the axis of its hinged connectionwith the upright duct, and further characterized by support means at thetop of the abrading head and fixed with respect to the axis of the belttensioning roll, and means on the hood seated upon said support means topositionally orient the hood with respect to the belt tensioning rolldespite variations in the elevation thereof.
 23. The abrading machine ofclaim 21, further characterized by deflector means at the inlet to thehood in close juxtaposition to the adjacent surface of the abrasivebelt, to intercept dust and products of abrasion traveling with the beltand direct the same into the hood.
 24. The abrading machine of claim 22,further characterized by deflector means at the inlet to the hood inclose juxtaposition to the adjacent surface of the abrasive belt, tointercept dust and products of abrasion traveling with the belt anddirect the same into the hood.